Found it... You must manually delete a file that AIR installed in your Mac's system audio Library directory.
Follow the Apple instructions at... https://support.apple.com/en-us/HT201532
Then move the hybrid.components file to the trash.
You can first do a Show Info on the file to confirm that it is from AIR Technologies. It is pretty old, around 2014 or so I think, so it needs updating.
After deleting the file, restart GarageBand.
I just got the Akai MPK Mini and found that the software doesn't seem to work on a Mac, including the MPK setup editor software that you use to configure the Mini. I suppose I'll try see if it works in Windows... Hey ho...
Good Luck!